The long-term objective of the proposed research is to understand the functional divergence and conservation of the sex-determination pathway in flies and other taxa. The first specific aim is to test the hypothesis that those components of the pathway that act last in the hierarchy are most likely to be conserved. The second specific aim is to study the evolutionary acquisition of molecular function. The third specific aim is to test competing hypothesis about the expected level of within species variation ingenues acting near the beginning of the sex-determination hierarchy, as compared with the level of within species variation in genes acting near the end of the hierarchy. The value of this research is that it will illuminate the process by which genetic pathways involve, and thereby produce a conceptual framework for applying knowledge of model systems like Drosophila to the development of the other organisms, including humans. The first two specific aims will be achieved by cloning and characterizing homologies of the intersex and determining mechanisms. To achieve the third specific aim, a mutation in hermaphrodite will be introgressed into a diverse set of wildtype fly strains, to uncover genetic variation in interacting genes involved in sex determination.